There are many situations where it is desirable to internally inspect long lengths of pipe which are already in place, either underground, in a building, or underwater. For example, sewer and drain pipes frequently need to be internally inspected to diagnose existing problems or determine if there are any breaks causing leakage or obstructions impairing the free flow of waste. It is also important to internally inspect steam pipes, heat exchanger pipes, water pipes, gas pipes, electrical conduits and fiber optic conduits for similar reasons. Frequently, pipes which are to be internally inspected have an internal diameter of six inches or less. It is sometimes necessary to inspect several hundred feet of pipe.
Over the years, video pipe inspection systems have been developed which typically include a camera which is forced down the pipe so that its interior can be viewed on a video display. It is common to record the inspection on a video recorder (VCR). Conventional video pipe inspection systems include a video push cable which provides an electromechanical connection between a rugged camera head enclosing and protecting the video camera and a rotatable push reel which is used to pay out cable and force the camera head down the pipe. The video push cable must be specially constructed in order to be flexible enough to make tight turns yet rigid enough to be pushed hundreds of feet down small diameter pipe. The video push cable must also incorporate electrically conductive cable having the proper impedance for conveying the NTSC or other video signals to the video display unit and additional power and ground conductors. Examples of video push cables are disclosed in U.S. Pat. No. 5,457,288 granted Oct. 10, 1995 to Mark S. Olsson and U.S. Pat. No. 5,808,239 granted Sep. 15, 1998 to Mark S. Olsson. Typically the camera head has a plurality of LEDs that illuminate the interior of the pipe or conduit so that the video camera can obtain a clear and well defined image.
The design of the video camera head and the manner in which it is connected to the distal end of the video push cable is critical to the performance and reliability of a video pipe inspection system. These structures must be rugged, yet the camera head must be compact and its manner of connection to the video push cable must be flexible enough to bend through tight turns. It is also desirable to incorporate an electromagnetic radiation transmitter near the video camera head so that its position can be confirmed with a remote above-ground locator instrument.
Prior commercial video pipe inspection systems have utilized a coil spring aft of the rigid video camera head to surround and protect the connection between the video push cable and the video camera head while providing the required flexibility. It has also been common to provide the camera head with radially extending vanes or bristles to center the camera head in the pipe. The mounting of a properly sized and positioned pipe guide on the video camera head ensures that the interior of the pipe is subjected to more even lighting from the LEDs and ensures that the field of view of the camera is centered along the central axis of the pipe. The pipe guide also gets the camera above any water or muck present at the bottom of the pipe to avoid smears on the protective lens of the camera head. Moreover, a pipe guide facilitates insertion and withdrawal of the video camera head, especially around corners in the pipe or conduit, and reduces wear and tear on the camera head, and in particular, scratching on its protective lens.
FIG. 1 is a diagrammatic illustration of a conventional video pipe inspection system 10. The forward or distal end of a video push cable 12 is coupled through an electromechanical termination assembly 14 to a rugged video camera head 16 which contains a compact black and white or color video camera that includes a charge-coupled device (CCD). A tubular stainless steel coil steel spring 18 surrounds the push cable 12 and is mechanically coupled to the rear end of the video camera head and to the termination assembly 14. The coil spring 18 provides the correct amount of flexibility to permit the video camera head 16 to negotiate tight turns when inserted down the interior of the pipe P. Stainless steel aircraft type cables 19 connects the camera head 16 to the termination assembly 14. The cables 19 limit the extension of the spring and facilitates removal of the camera head 16 if it were to get stuck in the pipe. A plurality of deformable fins 20 are spaced circumferentially around the camera head 16 and extend in radial directions. The fins 20 form a pipe guide that centers the camera head in the interior of the pipe. The push cable 12 is wound into a coil about a rotatable support reel 22. The rearward or proximal end of the push cable 12 is electrically connected through a slip ring assembly (not illustrated) to a signal transmission line 24 to the system electronics 26 that may include a video display screen. The camera head 16 can be pushed several hundred feet down the length of the pipe P. A ferrous element 27 is located inside the coil spring 18 and is driven with a suitable active drive signal from the system electronics 26. The active drive signal may have a frequency of, for example, 512 Hz. The resulting electromagnetic signal emitted by the ferrous element 27 can be sensed by the antennas of a conventional line and sonde locator so that the operator knows exactly which segment of the interior of the pipe P is being displayed. This tells the operator where the blockage or pipe defect is located.
It is not always desirable to permanently mount the fins 20 on the camera head 16. For example, this may increase the diameter of the camera head 16 too much to negotiate turns in the pipe P. Also, if the fins 20 are permanently connected, it may be impossible to withdraw the camera head 16 if the fins 20 become jammed in a bend in the pipe. Moreover, it is often beneficial to have two separate pipe guides mounted in longitudinally spaced locations. The camera head 16 has a short longitudinal dimension, and therefore it would be desirable to releasably mount a pipe guide around the tubular coil spring 18.
Split C—shaped steel rings have been used to externally clamp the cylindrical collar of a vaned guide around the coil spring of a video pipe inspection system aft of the camera head. Expanding locking sleeve assemblies have also been used inside the collars of vaned guides to clamp them around the coil spring of a video pipe inspection system aft of the camera head. These approaches are difficult to install and the guides may not break free if the camera head gets jammed in a pipe.